Red luminescent europium activated yttrium oxychloride phosphor and color television display tubes containing said phosphor

ABSTRACT

Europium activated red luminescing phosphor for color television, said phosphor being a trivalent europium activated oxychloride of an element such as a rare earth metal such as yttrium, lanthanum and gadolinium.

United States Patent [191 [111 3,723,787 Blasse et al. Mar. 27, 1973[54] RED LUMINESCENT EUROPIUM ACTIVATED YTTRIUM OXYCHLORIDE PHOSPI-IORAND COLOR TELEVISION DISPLAY TUBES CONTAINING SAID PHOSPIIOR Inventors:George Home; Jaap De Vries, both of Emmasingel, Eindhoven, NetherlandsAssignee: U.S. Philips Corporation, New

York, N.Y.

Filed: Mar. 6, 1970 Appl. No.: 17,013

Related U.S. Application Data Continuation of Ser. No. 654,652, July 19,1967, abandoned.

U.S. Cl ..313/92 PH, 252/3014 H Int. Cl. ..C09k 1/08, l-IOlj 29/20 Fieldof Search ..252/301.4; 313/92 [56] References Cited UNITED STATESPATENTS 2,729,605 l/1956 Swindells ..252/301 .4 3,415,757 12/1968Wanmaker et al. ....252/301.4

OTHER PUBLICATIONS Kroger-Luminescence of Solids 1948 pages 52, 291,292, 294, 295, & 296

Primary Examiner-Robert D. Edmonds Attorney-Frank R. Trifari [57]ABSTRACT 3 Claims, 1 Drawing Figure PATH-HEB m2 7 I975 3. 723' 787 l .-iV5. 5709. GEORGE BLASSE JAAP DE VRIES AGE RED LUMINESCENT EUROPIUMACTIVATED YTTRIUM OXYCIILORIDE PHOSPI'IOR AND COLOR TELEVISION DISPLAYTUBES CONTAINING SAID PHOSPHOR This application is a continuation of ourcopending United States patent application Ser. No. 654,652, filed July19, 1967 and now abandoned.

The invention in this case relates to a novel red luminescing phosphorand to a color television display tube provided with a luminescentscreen which contains this red phosphor.

Until a few years ago, color television display tubes nearly alwaysemployed a luminescent screen the red luminescing component of whichconsisted of a silveractivated sulphide of zinc and cadmium. Since a fewyears, this situation has changed owing to the discovery that manycompounds activated with trivalent europium, particularly compounds ofrare earth metals, show a red luminescence upon excitation by electrons.A few of these compounds, for example, yttrium vanadate, gadoliniumoxide and yttrium oxide, are more suitable for displaying colortelevision pictures than the sulphides. These compounds generally have ahigher lumen equivalent than the sulphides upon excitation by electrons.Since the emission is moreover concentrated in a narrow wavelengthrange, a more natural reproduction of deep-red colors can thus beobtained and the brightness of the entire color television picture canbe increased.

However, besides their favorable properties, these substances also havea few unfavorable properties. For

example, it is very difficult to obtain yttrium vanadate of a purelywhite color. Due to. the presence of nonconverted vanadium oxide, theconventional methods of preparation nearly always yield a gray coloredpowder. Although an improvement may be obtained in this respect bywashing the gray powder with a lye, for example, caustic soda, the colorof the washed substance becomes light-yellow. This light-yellow color isvery disadvantageous in color television display tubes, since it maygive rise to a color shift when the screen is struck by incident whitelight. Thus the yellow vanadate reflects the yellow radiation from thewhite light, so that the spectator observes a color that is a mixture ofthis yellow reflected light and the red luminescent light originatingfrom the vanadate. Of course, this phenomenon is very disturbing.Further, the additional process of washing with the lye renders thephosphors more expensive.

Also the oxides of yttrium and gadolinium cause difficulties in themanufacture of the luminescent screens for color television displaytubes. As they are soluble in water and diluted acids, an excess of saidsubstances, which is not left on the luminescent screen, can berecovered only with great difficulty. However, this recovery is verydesirable, since these substances are very expensive, incontradistinction to sulphides.

A further disadvantage of the suspensions of europium-activatedgadolinium oxide or yttrium oxide is that they produce an alkalinereaction, which has a disturbing effect during the application of thesesubstances to the display screen, since in such process, use isfrequently made of a photochemically hardening binder containingammonium bichromate. Due to the alkaline reaction of the suspension,this bichromate is readily converted into chromate which does notproduce the reaction desired for the hardening process.

According to our invention we have prepared a novel europium activatedphosphor wherein the above-stated disadvantages are substantiallycompletely obviated.

More particularly according to our inyention we have prepared a noveleuropium activated red luminescing phosphor of the formula Me ,,Eu, OCl,in which formula Me represents at least one of the elements of the groupcomprising yttrium, lanthanum and gadolinium and x has a value of 10' sx 0.15. According to another aspect of our invention we have provided acolor television display tube containing as the red luminescingcomponent the novel europium activated phosphor of our invention.

The europium content is chosen so that 10' x 0.15. For within theselimites, the efficiency is very high. The maximum efficiency is obtainedat values of x lying between 0.01 and 0.06.

Upon excitation by electrons, the europium activated phosphors of ourinvention exhibit an emission which is as red as that of the yttriumvanadate and redder than that of the gadolinium oxide.

Further the phosphors of our invention have a white color, do notproduce in suspension an alkaline reaction and are not soluble in waterand diluted acids.

The preparation of the phosphors according to the invention is simple. Aparticular advantage is that the heat treatment, which is alwaysrequired for all phosphors, can be carried out at a low temperature,i.e., at a temperature lying between 300 C and 700 C.

Upon excitation by electro'ns, gadolinium oxychloride and yttriumoxychloride have an energy efficiency of 4 percent and 3 percent,respectively. The efficiency of lanthanum oxychloride is slightly lower,i.e., approximately 2 percent.

Our invention will now be described in greater detail with reference tothe Drawing and example.

In the Drawing the sole FIGURE shows, partly in section, a cathode-raytube employing a red luminescent component of our invention. The tubeconsists of a cylindrical part 1 and a frusticonical part 2. The part 2is closed at one end with a face plate 3 of glass which is covered onits interior side with a luminescent screen 4. This screen consists ofan array of regulary placed dots which emit, upon electronic excitation,one of the colors green, blue or red. The red luminescing dots consistof a europium-activated yttrium oxychloride of our invention.

The luminescing dots may be bound to the glass plate by means of abinder for example polyvinyl alcohol hardened by ultraviolet radiation.

EXAMPLE 21.5 g of Y O and 1.8 g of Eu O are dissolved in concentratedhydrochloric acid and the compound Y Eu Cl .61-1 O is caused tocrystallize from this solution by heating. This compound is then heatedfor 6 hours in a current of oxygen at a temperature of 600 C. Thecompound is thus converted into the oxychloride having the formula Y EuOCl. This compound is immediately suitable to be applied to theluminescent screen of a color television display tube by means of theusual methods.

3,723,787 3 4 Instead of causing the water-containing chloride tophosphor of the formula or stallize from the solution in theconcentrated hy drochloric acid, the solution may be evaporated to [Mewocl dryness. The same compound is then obtained. wherein x has a valueThe oxychlorides of lanthanum or gadolinium may 5 be prepared in a quiteanalogous manner, but of course $015 the different atomic weights of theelements must then 2. The red luminescing phosphor of claim 1 wherein betaken into account. It is also possible to prepare ox- X g (106-ychlorides of two or more of the said elements, since 10 A p ytubecomammg as the they readily form mixed crystals. red luminescingphosphor a red luminescent phosphor What is claimed is: of clam 1. A redluminescing europium activated oxychloride

2. The red luminescing phosphor of claim 1 wherein 0.01 < or = x < or =0.06.
 3. A color television display tube containing as the redluminescing phosphor a red luminescent phosphor of claim 1.